Getting accurate white balance can be tough, especially when you have mixed light pouring into a scene. If you don't have professional white balance filter (like the Expodisc), you can still do pretty well with a regular old Starbucks coffee lid.

Photographer Steve Bennet discovered the lid—while not flawless—performed remarkably well as a white balancing tool. How does it work? Much like a proper white balance filter:

To use, I set the focus to infinity, place the [coffee lid] over, then set the custom WB. I dont even need to hold it as it fits nicely inside my lens hood, but that is just a lucky coincidence.

Some argue a bleached coffee filter is better, but that may be harder to come by in a pinch. The nice thing about Starbucks coffee lids is that they're always right down the street.